In our U.S. Pat. No. 4,070,612, issued Jan. 24, 1978, the disclosure of which patent is incorporated herein by reference, we disclose and claim a method of measuring terrain conductivity comprising generating an alternating current having a frequency F hertz, and applying the current to a transmitter for transmission to the terrain, receiving signals from the terrain by means of a receiver coil spaced from the transmitter coil above the terrain by a distance D of not more than about 50/.sqroot.FG where G is the highest terrain conductivity to be measured in siemens/meter, isolating the quadrature component of the received signal, and using the amplitude of said signal as a linear indicator of terrain conductivity. Apparatus for carrying out this method is also described, illustrated and claimed.